A floating dock of conventional type comprises a supporting bottom structure having side walls along its longitudinal sides for providing i.a. the necessary stability, when the dock is lowered. The bottom structure includes a number of displacement tanks, which are filled with water, when the dock is to be sunk, and which must be emptied when the dock is to be raised.
The pumps for handling the ballast water are usually located in the lower parts of the side walls, while their driving motors are accommodated higher up in the side walls, in spaces which during most of the working time will remain above water level. The transfer of torque is obtained by means of long, vertical shafts, for which it is difficult to provide satisfactory journalling and lubrication. The outlets from the pumps are directed horizontally outwards from the dock's sides.
In order to accommodate the lowered dock a well is often excavated in the sea-bed outside the quay or pier, where the dock is moored, and it is evident, that there is a big risk of such well being filled with mud and debris.
The most heavily stressed portion of the dock is located along the centre line of the bottom structure, and it is desirable to locally strengthen this portion.